Stepper motor gas valve and method of control

ABSTRACT

A controller for a variable heating system is operable to control a stepper motor operated gas valve to adjust gas flow to vary the heating level. The controller includes a first terminal for receiving a thermostat signal requesting heating, an electronic memory, and a microprocessor in communication with the electronic memory and first terminal. The microprocessor detects a thermostat signal requesting heating, and generates a control signal for the stepper motor to operate the gas valve. The microprocessor includes a programmable read-only-memory encoded with an instruction to store a time duration during which the microprocessor detects a thermostat signal requesting heating, and further encoded with an instruction operable to determine a desired heating level based on the stored time duration. The microprocessor responds to a thermostat signal requesting heating by determining the number of steps the motor must move to vary the gas flow corresponding to the desired heating level.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/228,474, filed on Jul. 24, 2009. The entire disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to systems for control of an applianceincorporating a flame, and more particularly relates to valve control ofa fuel to such an appliance.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

There are two types of commonly available, gas-fired, warm air furnacesin the marketplace: those with a single gas flow rate, and those withtwo or more gas flow rates. These are referred to as single andmultistage furnaces, respectively. Multistage furnaces are frequentlyselected by homeowners for replacement furnaces because they offerincreased performance and comfort. In retrofit applications there istypically an existing single stage thermostat and wiring in place. Itcan be troublesome to install a multistage thermostat in a retrofitapplication when a single stage thermostat is already in place becauseof the need to route additional wiring through walls for the additionalstages. For simple and economical installation, it is desirable to beable to continue to use a single stage thermostat and thermostat wiringwhen replacing a single stage furnace with a multistage furnace.

Several attempts have been made to allow a single stage thermostat towork with multi-stage furnaces. In some multi-stage furnaces, thefurnace control switches from a low heating level to a full capacityheating level after some pre-set time has expired, regardless of thelevel of heating actually required at the time. Accordingly, a needstill exists for an improved control of variable stage heating systems.

SUMMARY

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

Various embodiments of a controller for a variable output heatingapparatus are provided, which may be connected to either a single stageor a two-stage thermostat. One embodiment of a controller for a variableheating system is operable to control a stepper motor operated gas valveconfigured to adjust a gas flow rate to vary the level of heatingoperation. The controller includes a first terminal configured toreceive a thermostat signal requesting heating operation, an electronicmemory, and a microprocessor in communication with the electronic memoryand the first terminal. The microprocessor is configured to detect thepresence of a thermostat signal requesting heating at the firstterminal, and to generate a control signal for the stepper motoroperated gas valve to operate the gas valve for establishing heatingoperation. The microprocessor includes a programmable read-only-memoryencoded with an instruction to store in the electronic memory a timeduration during which the microprocessor detects the presence of athermostat signal requesting heating, and further encoded with aninstruction operable to determine a desired heating level based on thestored time duration. The microprocessor is configured to respond to thedetection of a thermostat signal requesting heating by determining thenumber of steps the stepper motor must move to adjust the gas valve to agas flow rate corresponding to the desired heating level. Themicroprocessor responsively generates a control signal corresponding tothe determined number of steps for the stepper motor to adjust the gasvalve to the gas flow rate corresponding to the desired heating level.

In another aspect of the present disclosure, various controllers may beutilized in combination with a stepper-motor controlled gas valve havinga main diaphragm in a main diaphragm chamber that controllably displacesa valve element relative to a valve opening. The main diaphragmdisplaces the valve element in response to changes in pressure in themain diaphragm chamber, to thereby adjust the flow of fuel through thevalve opening. The stepper-motor operated gas valve further includes aservo-regulator diaphragm configured to regulate fluid flow to the maindiaphragm chamber, which flow acts against the main diaphragm to adjustthe valve and vary the rate of fuel flow therethrough. The stepper motoris configured to move in a stepwise manner to displace theservo-regulator diaphragm for regulating fluid flow to the diaphragmchamber, to adjust the valve and thereby vary the rate of fuel flowthrough the valve.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic diagram showing one embodiment of a controller fora two-stage heat source according to the principles of the presentdisclosure;

FIG. 2 is a block system diagram illustrating the controller of astepper motor driven gas valve, according to the present disclosure;

FIG. 3 shows a perspective view and a schematic cut-away view of oneembodiment of a stepper-motor operated gas valve controller according tothe present disclosure;

FIG. 4 is a schematic diagram showing a second embodiment of acontroller for a variable heating system;

FIG. 5 shows a graph of the output of a variable rate gas valve andvariable capacity heating apparatus, according to the presentdisclosure; and

FIG. 6 shows a graph of the output of a variable rate gas valve andvariable capacity heating apparatus, according to the presentdisclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

In the various embodiments of the present invention, a controller for avariable heating apparatus is provided that is adapted to be connectedto either a single stage or a two-stage thermostat. In one embodimentshown in FIG. 1, a controller 20 is provided that comprises amicroprocessor 22 and a first terminal 24 for receiving a signalrequesting heating from a single-stage thermostat that may be connectedto the first terminal 24 via wire 40. When replacing a single stagefurnace with a variable heating capacity furnace 50, it is desirable tobe able to use an existing installed single stage thermostat andexisting wiring, because of the cost associated with routing additionalwiring through flooring 46 and walls 48 for the additional stages. Thepresent controller provides for control of a variable heating capacityfurnace using the existing single stage thermostat, based on the“request for heat” signal from the existing thermostat. When a requestfor heat signal from a thermostat is received at the first terminal thecontroller controls the stepper motor to operate the gas valve toestablish initial operation of the heating system. Thereafter, thecontroller 20 is configured to detect a thermostat signal requestingheating operation, and to determine a desired heating level based on atime period in which a signal at the first terminal was present in aprior heating cycle, to thereby adjust the level of heating operationdepending on the heating demand.

Referring to FIG. 1, the controller or control circuit 20 is coupled toa 24-volt power source 52, which supplies power to a microprocessor 22and also a stepper motor operated gas valve 100. The controller orcontrol circuit 20 further includes a first terminal 24 configured toreceive a thermostat signal requesting heating operation via connectionwire 42. Upon detecting the presence of a thermostat signal requestingheating operation at terminal 24, the microprocessor 22 is configured tocommunicate a control signal via 36 to the stepper-motor operated gasvalve 100 to establish low stage heating operation at a burner 58. Thecontroller 20 may further include a second terminal 26 configured toreceive a thermostat signal via 44 requesting high-stage heating. Upondetecting a thermostat signal requesting high stage heating operation,the microprocessor 22 is configured to communicate a control signal via36 to the stepper-motor operated gas valve 100 to supply gas via line 56for establishing a higher level of heating at a burner 58. The controlcircuit 20 is also configured to operate the variable capacity heatingapparatus between a minimum and maximum heating capacity depending onheating demand, as explained below.

Upon start-up of the heating apparatus or system, the microprocessor 22of the controller may be configured to control the initial operation ofa variable capacity heating apparatus to provide a low heating leveloperation (such as 40-65 percent of heating capacity). This initial lowheating level may be operated for a variable time period that is basedon heating demand, where the variable time period may be varied based ona duty cycle value indicative of heating demand, which is determined asfollows. The controller 20 includes a microprocessor 22 in communicationwith the first terminal 24, which accordingly can detect the presence ofa thermostat signal requesting heating operation at the first terminal24. The microprocessor 22 includes a programmable read-only memoryencoded with an instruction that is operable to store in an electronicmemory 30 the duration of time in which the signal at the first terminal24 is present. The microprocessor 22 may be further configured tocalculate a duty cycle value based on the ratio of the duration of timein which a signal requesting or calling for heat is present at the firstterminal 24 versus the on and off time of a heating cycle. For example,a duty cycle value of 80 percent is calculated where a 10 minuteduration of heating operation was followed by a 2 minute off periodbefore the start of the next heating cycle, to yield 10 minutes onduring a 12 minute on-off heat cycle. The microprocessor 22 isconfigured to determine a low heating level time limit value 28 (shownin FIG. 5) from the calculated duty cycle value. Alternatively, the lowheating level time limit value 28 may be a default time period, such asan adjustably set time period of between 10 minutes and 20 minutes.Initially, absent any calculated duty cycle value or first stage timelimit value, the microprocessor may use a default time limit value, suchas 15 minutes for example.

In the various embodiments, the initial low level of heating operationis maintained until the expiration of the variable time period. Wherethe variable capacity heating apparatus is first operated (such as afterinstallation or at the beginning of a heating season), when the variabletime period expires the heating level is increased to 100% operatingcapacity. The stepper-motor moves the servo-regulator diaphragm to causethe valve to be fully opened to permit maximum gas flow, which ismaintained until the thermostat ceases to signal or call for heatingoperation, at which point heating operation terminates.

According to another aspect of the present disclosure, the variablecapacity heating apparatus may be operated between a minimum and maximumheating capacity depending on a duration of time that the heating systemoperated in one or more previous heating cycles. The microprocessor 22includes a programmable read-only memory encoded with an instructionthat is configured to determine and store in an electronic memory theduration of time in which the signal at the first terminal 24 ispresent. The microprocessor's programmable read-only memory is furtherencoded with an instruction configured to determine a desired heatinglevel based on the stored period of time in which a signal was presentat the first terminal 24 (e.g., the time that the variable capacityheating apparatus operated in a prior heating cycle). When a thermostatsignal requesting heating is detected, the microprocessor 22 isconfigured to control the stepper motor to adjust the valve to establishthe desired heating level determined by the microprocessor, to therebyadjust the level of heating operation based on heating demand, asexplained below.

After conclusion of the initial heating cycle, the microprocessor 22 isconfigured to detect the presence of a thermostat signal requestingheating at the first terminal 24. As previously stated, themicroprocessor 22 includes a programmable read-only memory encoded withan instruction to store the time duration in which the microprocessor 22detects the presence of a thermostat signal requesting heating via thefirst terminal 24. The microprocessor's programmable read-only memory isfurther encoded with an instruction configured to determine a desiredheating level based on the stored period of time (e.g., the time thatthe variable capacity heating apparatus operated in a prior heatingcycle). For example, if during an initial heating cycle the heatingapparatus operated for a time of six minutes (at which time thethermostat signal to the first terminal 24 was discontinued), themicroprocessor 22 includes an instruction that is configured todetermine a new desired heating level by decrementing the level ofheating operation by a predetermined percentage for each minute that theheating apparatus ran less than a threshold time period. The thresholdtime period may be a nominal operating time, which may in the range ofbetween about 8 minutes to about 20 minutes. If, in this example, theheating apparatus operated for only 6 minutes (4 minutes less than the10 minute threshold time period), the microprocessor 22 is configured todetermine a new desired heating level by decrementing the heating levelby 5 percent for each minute of operation less than the threshold timeperiod, or 20 percent from the 100% capacity heating level of the priorcycle. Thus, where the heating apparatus was initially operated at 100percent capacity for six minutes, the next call for heat would result inthe heating apparatus operating at 80 percent capacity. If, in the aboveexample, the heating apparatus was operated at 80 percent capacity forseven minutes, at the next call for heat the microprocessor 22 isconfigured to determine a new desired heating level by decrementing theprior heating level by 5 percent for each minute of operation under thethreshold time period, i.e., a 15 percent decrease from the 80 percentcapacity heating level in the previous cycle. Thus, the next call forheat would result in the heating apparatus operating at a heating levelof 65 percent capacity. Likewise, the microprocessor 22 may beconfigured to increment the level of heating operation in the nextheating cycle, by a predetermined percentage for each minute that theheating operation exceeds a threshold time period (such as 10 minutes).If the heating apparatus in the above example were operated at 65%capacity for 13 minutes (3 minutes longer than the 10 minute thresholdtime period), the microprocessor 22 is configured to determine a newdesired heating level by incrementing the prior heating level by 5percent for each minute of operation over the threshold time period,i.e., a 15 percent increase above the heating level from the previouscycle. Thus, the next call for heat would result in the heatingapparatus operating at a heating level that is at 80 percent capacity.

The microprocessor 22 may be further configured to increment the levelof heating operation by a predetermined percentage whenever the heatingapparatus is operated continuously for more than a threshold time period(such as 10 minutes). For example, where the heating apparatus isoperated longer than 10 minutes, the microprocessor 22 may increment thelevel of heating by 20 percent. Where the controller 20 is connected toa two-stage thermostat via the second terminal 26, the microprocessor 22may be configured to receive a second stage heating signal (from atwo-stage thermostat requesting 100 percent heating capacity operationvia second terminal 26) and responsive increment the level of heatingoperation by a predetermined amount (such as 20 percent, for example).

Thus, the microprocessor 22 may be configured to determine a desiredlevel of heating based on the duration of time that the heatingapparatus was operated in at least one prior heating cycle, and mayaccordingly adjust the level of heating as needed when heating operationis requested or called for by a thermostat or system control. It shouldbe noted that the microprocessor 22 may be configured to average two ormore prior heating cycle time durations, and determine a new level ofheating based on the average of two or more heating cycle timedurations. For example, the microprocessor 22 may be configured todetermine a desired level of heating operation based on the followingformula:

% change to prior capacity=(prior on-time(min)−thresholdon-time(min))×5%,

where the desired level of heating operation is the previous level ofheating with the above calculated offset percentage.

Operation of the controller 20 and microprocessor 22 is shown in theschematic in FIG. 2, which shows the determination of a desired heatinglevel or rate of gas flow (within minimum and maximum limits), based onthe present on time that the heating apparatus is operated. Thecontroller 20 may also increment the level/rate of operation by 20percent upon receiving a “W2” second stage signal from a two-stagethermostat via second terminal 26 (see FIGS. 1-2).

Referring to FIG. 3, a stepper-motor operated gas valve 100 is shown.The stepper-motor operated gas valve 100 includes a main diaphragmchamber 102, and a main diaphragm 104 disposed in the main diaphragmchamber. The main diaphragm controllably displaces a valve 106 relativeto a valve opening 108 in response to changes in pressure in the maindiaphragm chamber 102, to thereby permit adjustment of the flow of fuelthrough the valve opening. The stepper-motor operated gas valve 100further includes a servo-regulator diaphragm 110, which is configured toregulate fluid flow to the main diaphragm chamber. The servo-regulatordiaphragm therefore controls the fluid pressure applied to the maindiaphragm, to control the rate of fuel flow through the valve opening.The stepper-motor operated gas valve 100 also includes a stepper motor120 configured to move in a stepwise manner to displace theservo-regulator diaphragm 110, for regulating fluid flow to thediaphragm chamber 102 to thereby regulate the rate of fuel flow throughthe valve.

The stepper-motor accordingly provides control over the extent ofopening of the valve 108, to provide modulated fuel flow operation. Thefirst embodiment of a gas valve 100 is governed by a stepper motor 120.The stepper-motor operated gas valve control 100 preferably includes acontroller 130 (see control circuit 20 shown in FIG. 1) that includesthe microprocessor 22 (shown in FIG. 1). The controller 130 isconfigured to receive an input control signal via a first terminal 24requesting heating operation (such as from a thermostat or heatingsystem control).

The microprocessor 22 is configured to determine a select motor stepvalue that corresponds to the desired level of heating operationdetermined based on the prior on-time value, and to move thestepper-motor 120 a number of steps corresponding to the desired levelof heating operation, which displaces the servo-regulator diaphragm 110and valve element to thereby control the rate of fuel flow through thevalve opening. The microprocessor 22 determines the number of steps themotor must turn or move to set the servo-regulator diaphragm to therequested fuel level. The stepper motor gas valve 100 drives thestepper-motor 120 in a step-wise manner, to the desired stepper motorposition, which causes the stepper-motor to displace the servo-regulatordiaphragm the desired distance and thereby regulate the output of thevalve.

The microprocessor 22 may be configured to initiate operation of aheating apparatus at a low level of heating (such as 65 percent ofcapacity) for a given initial time period 28 (shown in FIG. 5), afterwhich the microprocessor 22 determines a desired heating level thatresults in incrementing the initial level by 5 percent. After 10 minutesof operation, the microprocessor 22 is configured to increment the levelof heating by a predetermined amount (such as 20 percent), which resultsin operation as 90 percent capacity. After 12 minutes of continuousoperation, the thermostat call for heat is discontinued and the heatingcycle terminates. At the next call for heat, the microprocessor 22 isconfigured to determine a value for at least one prior heating cycleduration (which may be the average of two or more cycles), and toincrement the prior rate of 70 percent capacity to 90 percent capacitybased on the 4 minutes of operation beyond the 10 minute targetthreshold. On the third call for heat, the microprocessor determines adesired level of heating based on a prior heating cycle of 9 minutes,and decrements the 90 percent operation level from the prior cycle by 5percent to 85 percent.

In use, the controller 130 and stepper-motor operated gas valve 100would be included within a fuel-fired heating system 200 that includes aburner 258 (as shown in FIG. 4), which is supplied with fuel by thestepper-motor operated gas valve 100. The fuel-fired heating system 200further includes a thermostat (not shown in FIG. 4) that communicateswith the system or furnace controller 230 for controlling operation of astepper-motor operated gas valve.

In the above embodiment, a controller 130 is provided for controlling astepper motor gas valve, in which the stepper motor, gas valve, andcontroller 130 are all part of a combined controller and gas valveproduct that are integrally manufactured or assembled as a unit. Itshould be understood that the above stepper-motor operated gas valveutilizes a set of motor step values that correspond to a plurality ofpositions of the stepper motor for adjusting the gas valve, whichpositions range between a closed no-flow position to a 100% fullcapacity position. The above described embodiment of a controller 130and stepper-motor operated gas valve 100 may be employed in combinationwith a single stage or two-stage thermostat and a burner that issupplied with fuel by the stepper-motor operated gas valve control 100,where the thermostat simply requests initiation of heating and thecontroller 130 is configured to determine the desired heating rate.

Alternatively, in a second embodiment shown in FIG. 4, the control of avariable rate gas valve in accordance with the principles of the presentdisclosure is provided by a system or furnace controller 230 forcontrolling a variable rate gas valve of a variable heating system,where the system or furnace controller 230 determines the desiredheating rate.

Referring to FIG. 4, the system or furnace controller 230 is coupled toa 24-volt power source 252, which supplies power to microprocessor 222and also a stepper motor operated gas valve 100. The system or furnacecontroller 230 includes a first terminal 224 configured to receive athermostat signal requesting heating operation via connection wire 240passing through the flooring 246 and walls 248 of a space. Upondetecting the presence of a thermostat signal requesting heatingoperation at terminal 224, the microprocessor 222 is configured tocommunicate a control signal via 236 to the stepper-motor operated gasvalve 100 to establish low stage heating operation at a burner 258. Thesystem or furnace controller 230 may further include a second terminal226 configured to receive a thermostat signal via 244 requestinghigh-stage heating. Upon detecting a thermostat signal requesting highstage heating operation, the microprocessor 222 is configured tocommunicate a control signal via 236 to the stepper-motor operated gasvalve 100 to supply gas via line 256 for establishing a higher level ofheating at a burner 258. The system or furnace controller 230 isconfigured to operate the variable capacity heating apparatus between aminimum and maximum capacity depending on demand, as explained below.

In the second embodiment, the system or furnace controller 230 isconfigured to generate a gas valve control signal that is input to avariable rate gas valve that supplies a burner 258 with fuel. The systemor furnace controller 230 may be configured to generate a gas valvecontrol signal in the form of a pulse-width modulating signal or aserial communication signal for controlling either a stepper motoroperated gas valve or a modulating solenoid operated gas valve. Wherethe variable rate gas valve is a stepper motor operated gas valve, thestepper motor operated valve 100 includes a third terminal 228 thatreceives the control signal generated by the system or furnacecontroller 230. Alternatively, the control signal may be in the form ofa milliamp signal for controlling either a stepper motor operated gasvalve or a modulating solenoid operated gas valve. One such example of amodulating gas valve is disclosed in U.S. Pat. No. 6,705,342, thedisclosure of which is incorporated herein by reference. Where thevariable rate gas valve is a modulating solenoid operated gas valve, themodulating solenoid operated gas valve includes a ‘V’ terminal thatreceives the control signal generated by the system or furnacecontroller 230, and causes a variable valve displacement based on thevalue of the milliamp signal. In each of the above control signals, thesystem or furnace controller 230 is configurable to generate a controlsignal for a select variable rate gas valve that corresponds to adetermined desired heating level.

Upon start-up of the variable heating system shown in FIG. 4, themicroprocessor 222 of the system or furnace controller 230 is configuredto detect a thermostat signal requesting heating via an input terminal224 and to generate a control signal for operating the variable rate gasvalve to initial operation of the variable capacity heating apparatus toprovide a low heating level operation (such as 40-65 percent of heatingcapacity). This initial low heating level may be operated until thethermostat signal requesting heating operation is discontinued. As anexample, the microprocessor 222 may generate a control signal foroperating the variable rate gas valve to establish low heating leveloperation at 65 percent of heating capacity for a time period of 11minutes (at which time the thermostat discontinues the signal to inputterminal 224).

After the initial heating cycle, the system or furnace controller 230 isconfigured to respond to subsequent thermostat signals requestingoperation in subsequent heating cycles by starting the variable capacityheating apparatus at a low heating level (such as 65 percent of heatingcapacity) and shortly thereafter generating a control signal to thevariable rate gas valve to provide a desired heating level that is basedon a duration of time that the heating system operated in one or moreprevious heating cycles, as explained below.

According to one aspect of the present disclosure, the microprocessor222 includes a programmable read-only memory encoded with an instructionthat is operable to determine and store in an electronic memory theduration of time in which the microprocessor 222 detects the presence ofa thermostat signal requesting heating operation at the input terminal224. The microprocessor's programmable read-only memory is furtherencoded with an instruction operable to determine a desired heatinglevel based on the stored time duration in which a thermostat signal waspresent at the input terminal 224 (e.g., the time that the variablecapacity heating apparatus operated in a prior heating cycle). Afterconclusion of the initial heating cycle, the microprocessor 222 isconfigured to respond to the detection of a thermostat signal requestingheating at the input terminal 224 by determining a desired heating leveland generating a corresponding control signal for controlling thevariable rate gas valve to adjust the gas flow rate to the desiredheating level.

As in the previous embodiments, the microprocessor 222 includes aprogrammable read-only memory encoded with an instruction that isoperable to determine a desired heating level based on the stored timeduration in which a thermostat signal was present at the input terminal224 (e.g., the time that the variable capacity heating apparatusoperated in a prior heating cycle). For example, if in the above examplethe heating apparatus operated at 65 percent capacity in the initialheating cycle for a time of 11 minutes (after which the thermostatsignal to the input terminal 224 was discontinued), the microprocessor'sencoded instruction is configured to determine a new desired heatinglevel by incrementing the prior level of heating operation by apredetermined percentage for each minute that the heating apparatus ranlonger than a threshold time period. The threshold time period may be anominal operating time, which may in the range of between about 8minutes to about 20 minutes, and more preferably about 10 minutes. Inthis example, since the heating apparatus operated for 11 minutes (1minute longer than the 10 minute threshold time period), themicroprocessor 222 is configured to determine a new desired heatinglevel by incrementing the prior heating level by 5 percent for eachminute of operation above the threshold time period (e.g., 70 percentcapacity).

Referring to FIG. 5, a graph is shown of an example illustrating anumber of heating cycles as controlled by the system or furnacecontroller 230 of FIG. 4. In this example of controller operation, thesystem or furnace controller 230 responds to a thermostat signalrequesting heating by starting the variable capacity heating apparatusat a low heating capacity (e.g., 65 percent of heating capacity) andshortly thereafter generating a control signal to the variable rate gasvalve to provide a desired heating level of 70 percent capacity (basedon the capacity and duration of prior heating cycle, as in the aboveexample). If the heating apparatus operated at 70 percent capacity in aheating cycle that lasted 14 minutes (4 minutes longer than the 10minute threshold time period), the microprocessor 222 is configured todetermine a new desired heating level as explained below.

In the above example, the microprocessor's encoded instruction areoperable to store in an electronic memory the 14 minute duration of timein which the microprocessor 222 detects the presence of the thermostatsignal requesting heating, and further operable to determine a desiredheating level based on the stored time duration. Specifically, themicroprocessor's encoded instruction is operable to increment the prior70 percent heating level by 5 percent for each minute of operation overthe 10 minute threshold time period, resulting in a 20 percent increaseover the 70 percent capacity heating level. Thus, the next call for heatwould result in the heating apparatus operating at a heating level thatis at 90 percent capacity, as shown in FIG. 5.

The system or furnace controller 230 responds to a thermostat signalrequesting heating by starting the variable capacity heating apparatusin a subsequent heating cycle shown in FIG. 5, at 90 percent of heatingcapacity lasting only 9 minutes (1 minute less than the preferred 10minute threshold time period). The microprocessor's encoded instructionare operable to store in an electronic memory the 9 minute duration oftime in which the presence of the thermostat signal requesting heatingwas detected, and further operable to determine a desired heating levelbased on the stored time duration. Specifically, the microprocessor'sencoded instruction is operable to decrement the prior 90 percentheating level by 5 percent for each minute of operation less the 10minute threshold time period, resulting in a 5 percent decrement fromthe 90% capacity heating level of the prior cycle. Thus, the next callfor heat would result in the heating apparatus operating at 85 percentcapacity.

As shown in FIG. 4, a system or furnace controller 230 is utilized incombination with a variable rate gas valve, which may be a stepper motoroperated gas valve 100. The stepper-motor operated gas valve 100 issimilar to that shown in FIG. 3, and includes a main diaphragm chamber102, and a main diaphragm 104 disposed in the main diaphragm chamber.The main diaphragm controllably displaces a valve 106 relative to avalve opening 108 in response to changes in pressure in the maindiaphragm chamber 102, to thereby permit adjustment of the flow of fuelthrough the valve opening. The stepper-motor operated gas valve 100further includes a servo-regulator diaphragm 110, which is configured toregulate fluid flow to the main diaphragm chamber. The servo-regulatordiaphragm therefore controls the fluid pressure applied to the maindiaphragm, to control the rate of fuel flow through the valve opening.The stepper-motor operated gas valve 100 also includes a stepper motor120 configured to move in a stepwise manner to displace theservo-regulator diaphragm 110, for regulating fluid flow to thediaphragm chamber 102 to thereby regulate the rate of fuel flow throughthe valve. As previously stated, the stepper motor operated valve 100preferably includes a third terminal 228, which is configured to receivea control signal input from the system or furnace controller 230, asdescribed below.

In the second embodiment, the system or furnace controller 230 isconfigured to respond to the detection of a thermostat signal requestingheating by determining a desired heating level as described above, andfurther configured to generate a control signal for the variable rategas valve. The control signal may comprise a modulating signal input,which may be a pulse width modulation (PWM) signal having an on-offduty-cycle/frequency corresponding to an operating capacity level forthe desired heating level. Alternatively, the control signal may be inthe form of a serial communication signal or a milliamp signal forcontrolling the stepper motor operated gas valve. The stepper motoroperated valve 100 shown in FIG. 3 is configured to receive the controlsignal at the third terminal 228, and to determine the number of stepsthe stepper motor must move to adjust the gas valve to a flow ratecorresponding to the desired heating level. The stepper motor operatedgas valve 100 directs the stepper motor to displace the servo-regulatordiaphragm 110 and valve element to thereby establish a desired rate offuel flow through the gas valve 100 that corresponds to the controlsignal from the system or furnace controller 230. In this manner, thesystem or furnace controller 230 is configured to generate a controlsignal corresponding to a desired heating rate, as determined accordingto the above described principles.

Accordingly, the second embodiment includes a system or furnacecontroller 230 for a variable heating system having a variable rate gasvalve (such as a stepper motor operated gas valve 100 or modulatingsolenoid gas valve) for adjusting gas flow rate to vary the level ofheating. The system or furnace controller 230 includes a first inputterminal 224 configured to receive a thermostat signal requestingheating operation, and an electronic memory 232. The system or furnacecontroller 230 includes a microprocessor 222 in communication with theelectronic memory 232 and first input terminal 224, which is configuredto detect the presence of a thermostat signal requesting heating at thefirst input terminal 224 and to generate a control signal for thestepper motor operated gas valve 100. The microprocessor 222 includes aprogrammable read-only-memory that is encoded with an instruction tostore in the electronic memory 232 a time duration during which themicroprocessor 222 detects the presence of a thermostat signalrequesting heating, and further encoded with an instruction operable todetermine a desired heating level based on the stored time duration. Forexample, the microprocessor 222 may be configured to determine a newdesired heating level by decrementing the heating level of the priorheating cycle by 5 percent for each minute of operation under thepredetermined threshold time period. Similarly, the microprocessor 222may be configured to increment the level of heating operation by apredetermined percentage for each minute that the heating apparatusoperated beyond the threshold time period. The microprocessor 222 isconfigured to respond to the detection of a thermostat signal requestingheating by determining a signal value related to adjusting the variablerate gas valve (e.g., PWM signal having a duty cycle of on time versuson-off time of between 40% and 100% that is representative of capacity,or milliamp signal between 40 milliamps and 500 milliamps, for example)and generating a control signal to adjust the variable rate gas valve toestablish a gas flow rate corresponding to the desired heating level.The system or furnace controller 230 may be configured to determine thesignal value for adjusting the variable rate gas valve by selecting avalue from a look-up table corresponding to the desired heating level.

Accordingly, the system or furnace controller 230 is configured todetect the presence of a thermostat signal at an input terminal 224 andconfigured to determine a desired heating level by incrementing ordecrementing a prior heating level based on a stored duration of time inwhich the microprocessor 222 detected the presence of a thermostatsignal at the input terminal 224 from a prior heating cycle. Forexample, the microprocessor 222 may be configured to determine a desiredlevel of heating operation based on the following formula:

% change to prior capacity=(prior on-time(min)−thresholdon-time(min))×5%

where the level of heating operation or gas valve rate of flow isdetermined as the previous level or flow rate plus theincrement/decrement as determined above.

It should be noted that the microprocessor 222 may be configured toaverage two or more prior heating cycle time durations, and determine anew level of heating based on the average of two or more heating cycletime durations.

The system or furnace controller 230 may be connected to either asingle-stage thermostat, or alternatively a two-stage thermostat. Wherethe thermostat is a two-stage thermostat, the system or furnacecontroller 230 may be further configured to increase the prior level ofheating operation by 20 percent, if the system or furnace controller 230detects a signal at the second terminal 226 from the two-stagethermostat requesting second-stage heating operation. Where the systemor furnace controller 230 is connected to a two-stage thermostat via thesecond terminal 226, the microprocessor 222 may be configured to receivea second stage heating signal (from a two-stage thermostat requesting100 percent heating capacity operation). The microprocessor 222 may beconfigured to increment the level of heating operation by apredetermined percentage whenever the microprocessor detects athermostat signal requesting second stage heating operation. Forexample, where the heating apparatus has operated for a given time atfirst stage heating capacity, and the microprocessor 222 detects athermostat signal requesting second stage heating operation, themicroprocessor 222 may be configured to increment the prior level ofheating by a predetermined percentage, such as 20 percent, for example.

Referring to FIG. 6, a graph is shown of an example illustrating anumber of heating cycles as controlled by the system or furnacecontroller 230 of FIG. 4, which is further configured to automaticallyincrement the heating level after a predetermined time. In this example,the system or furnace controller 230 responds to a thermostat signalrequesting heating by starting the variable capacity heating apparatusat a low heating capacity (e.g., 65 percent of heating capacity) andshortly thereafter generating a control signal to the variable rate gasvalve to provide a desired heating level of 70 percent capacity (basedon the capacity and duration of prior heating cycle, as in the aboveexample). The microprocessor 222 may be further configured toautomatically increment the level of heating operation during any activeheating cycle in which the heating apparatus has operated for more thana predetermined threshold time period (such as the preferred thresholdtime period of 10 minutes, for example). As shown in FIG. 6, where theheating apparatus has operated at 70 percent operating capacity for a 10minute time, the system or furnace controller 230 is configured toautomatically increment the present level of heating by a predeterminedpercentage, such as 20 percent. Thus, the heating apparatus wouldoperate at 90 percent operating capacity until the end of the heatingcycle 4 minutes later (at which time the thermostat signal requestingheating is discontinued).

In view of the above described embodiments, systems and thermostats, thevarious controllers are configured such that each time the stepper-motoroperated gas valve is opened, the microprocessor may incrementally movethe stepper-motor to provide an initial low pressure supply of fuel andwithin a short interval thereafter move the stepper motor to adjust thesupply of fuel corresponding to a desired heating level determinedaccording to the above principles. It should be noted that the initiallow heating level may be operated for a variable time period that isbased on a duty cycle value indicative of heating load demand, or adefault time period, as described in the first embodiment. Accordingly,the various embodiments of a controller for a stepper motor driven gasvalve are configured to detect the presence of a signal at the firstterminal (e.g., receive a signal from a thermostat via the firstterminal requesting heating operation) and establish an initial heatinglevel at the beginning of a heating cycle, and further configured todetermine a desired heating level based on the duration of time in whicha signal at the first terminal is present in at least one prior heatingcycle.

It will be understood by those skilled in the art that the abovevariable capacity heating apparatus controller may be employed invarious types of heating systems with any combination of the abovedisclosed features, without implementing the others. It will beunderstood that the stepper motor driven gas valve and controllerdescribed above may be utilized in other forms of heating and coolingequipment, including water heater and boiler appliances. Accordingly, itshould be understood that the disclosed embodiments, and variationsthereof, may be employed without departing from the scope of theinvention.

1. A controller for a variable heating system having a variable rate gasvalve configured to adjust a gas flow rate to vary the level of heatingoperation, the controller comprising: a first terminal configured toreceive a thermostat signal requesting heating operation; an electronicmemory; and a microprocessor in communication with the electronic memoryand the first terminal, the microprocessor being configured to detectthe presence of a thermostat signal requesting heating at the firstterminal and to generate a control signal for the variable rate gasvalve to operate the gas valve for establishing heating operation, themicroprocessor including a programmable read-only-memory encoded with aninstruction to store in the electronic memory a time duration duringwhich the microprocessor detects the presence of a thermostat signalrequesting heating, and further encoded with an instruction operable todetermine a desired heating level based on the stored time duration,wherein the microprocessor is configured to respond to the detection ofa thermostat signal requesting heating by determining the desiredheating level, and generating a gas valve control signal correspondingto the desired heating level that is applied to the variable rate gasvalve to adjust the variable rate gas valve to the gas flow ratecorresponding to the desired heating level.
 2. The controller of claim1, wherein the instruction is configured to determine a new desiredheating level by decrementing the heating capacity level of the lastheating cycle by a predetermined percentage for each minute the storedtime duration of the signal requesting heating is less than a thresholdtime period.
 3. The controller of claim 1, wherein the instruction isconfigured to determine a new desired heating level by incrementing theheating capacity level of the last heating cycle by a predeterminedpercentage for each minute the stored time duration of the signalrequesting heating exceeds a threshold time period.
 4. The controller ofclaim 2 or 3, wherein the threshold time period is a time period in therange of between about 8 minutes and about 20 minutes.
 5. The controllerof claim 1, wherein the instruction is configured to determine a newdesired heating level based on the following formula:% change to prior capacity=(prior on-time(min)−thresholdon-time(min))×5%
 6. The controller of claim 5, wherein the threshold ontime period is a time period of about 10 minutes.
 7. The controller ofclaim 1 wherein the microprocessor is configured to determine a controlsignal value for adjusting the variable rate gas valve by selecting avalue from a look-up table corresponding to the desired heating level.8. The controller of claim 1 further comprising a second terminal forreceiving a signal for second stage heat operation from a two-stagethermostat connected to the second terminal, where upon receiving asignal via the second terminal, the microprocessor is configured toincrement the level of heating operation by a predetermined amount.
 9. Acontroller for a variable heating system having a variable rate gasvalve configured to adjust a gas flow rate to vary the level of heatingoperation, the controller comprising: a first terminal configured toreceive a thermostat signal requesting heating operation; an electronicmemory; and a microprocessor in communication with the electronic memoryand the first terminal, the microprocessor being configured to detectthe presence of a thermostat signal requesting heating at the firstterminal and to generate a control signal for the variable rate gasvalve to operate the gas valve for establishing heating operation, themicroprocessor including a programmable read-only-memory encoded with aninstruction to store in the electronic memory a time duration duringwhich the microprocessor detects the presence of a thermostat signalrequesting heating, and further encoded with an instruction operable todetermine a desired heating level based on the stored time duration, bydecrementing the heating capacity level of the last heating cycle by apredetermined percentage for each minute that the stored time durationis less than a threshold time period, or by incrementing the heatingcapacity level of the last heating cycle by a predetermined percentagefor each minute that the stored time duration exceeds a threshold timeperiod, wherein the microprocessor is configured to respond to thedetection of a thermostat signal requesting heating by determining thedesired heating level, and generating a gas valve control signalcorresponding to the desired heating level that is applied to thevariable rate gas valve to adjust the variable rate gas valve to the gasflow rate corresponding to the desired heating level.
 10. The controllerof claim 9, wherein the threshold time period is a time period in therange of between about 8 minutes and about 20 minutes.
 11. Thecontroller of claim 9, wherein the instruction is configured todetermine a new desired heating level based on the following formula:% change to prior capacity=(prior on-time(min)−thresholdon-time(min))×5%
 12. The controller of claim 11, wherein the thresholdon time period is a time period of about 10 minutes.
 13. The controllerof claim 9 wherein the microprocessor is configured to determine acontrol signal value for adjusting the variable rate gas valve byselecting a value from a look-up table corresponding to the desiredheating level.
 14. The controller of claim 13 wherein the signal valuerelated to adjusting the variable rate gas valve is a pulse widthmodulated signal having a duty cycle in the range of between 40 percentand 100 percent.
 15. The controller of claim 13 wherein the signal valueis a milliamp signal in the range of between about 40 milliamps andabout 500 milliamps.
 16. The controller of claim 13, wherein the controlsignal is a serial communication signal.
 17. The controller of claim 9,wherein the variable rate gas valve is a stepper motor operated gasvalve.
 18. The controller of claim 18, wherein the microprocessor isconfigured to determine the number of steps the stepper motor must moveby selecting a motor step value from a look-up table corresponding tothe desired heating level.
 19. The controller of claim 9 furthercomprising a second terminal for receiving a signal for second stageheat operation from a two-stage thermostat connected to the secondterminal, where upon receiving a signal via the second terminal, themicroprocessor is configured to increment the level of heating operationby a predetermined amount.
 20. A controller in combination with astepper-motor operated gas valve configured to vary the gas flow ratefor varying the level of heating operation, the controller andstepper-motor operated gas valve combination comprising: a valve elementmovable relative to a valve opening in the gas valve; a main diaphragmchamber disposed in the gas valve, a main diaphragm disposed in the maindiaphragm chamber and coupled to the valve element, the main diaphragmbeing configured to controllably displace the valve element relative tothe valve opening in response to changes in gas pressure acting againstthe main diaphragm; a servo-regulator diaphragm configured to regulateflow of gas to the main diaphragm chamber that acts against the maindiaphragm, to thereby adjust the valve element to vary the flow rate ofgas through the valve opening; a stepper motor configured to move in astepwise manner to displace the servo-regulator diaphragm for varyingthe flow of gas to the diaphragm chamber, to thereby control the rate ofgas flow through the valve opening; a first terminal disposed on the gasvalve configured to receive a control signal corresponding to a desiredgas flow rate for establishing a desired level of heating operation; afirst terminal on the controller configured to receive a thermostatsignal requesting heating operation; an electronic memory associatedwith the controller; and a microprocessor in communication with theelectronic memory and the first terminal, the microprocessor beingconfigured to detect the presence of a thermostat signal requestingheating at the first terminal and to generate a control signal for thestepper motor operated gas valve to displace the servo-regulatordiaphragm to establish gas flow for establishing heating operation, themicroprocessor including a programmable read-only-memory encoded with aninstruction to store in the electronic memory a time duration duringwhich the microprocessor detects the presence of a thermostat signalrequesting heating, and further encoded with an instruction operable todetermine a desired heating level based on the stored time duration,wherein the microprocessor is configured to respond to the detection ofa thermostat signal requesting heating by determining the number ofsteps the stepper motor must move to displace the servo-regulatordiaphragm and vary the gas flow rate corresponding to the desiredheating level, and to generate a control signal corresponding to thedetermined number of steps for the stepper motor to adjust theservo-regulator diaphragm and vary the gas flow rate corresponding tothe desired heating level.